1. Field of the Invention
The present invention relates to heat sink structures and, more articularly, to stacked heat sink structures with central openings and methods for making same.
2. Background and Related Art
The electronics industry is continuously endeavoring to reduce both the size of electronic packages and the pitch between conductive I/O contacts in order to accommodate the higher counts coming from higher density chips. With increased speed and miniaturization comes increased heat generation and its attendant problems, such as, increased failure rate of solder joints during temperature cycling due to the higher strain levels at the joints.
To reduce the levels of heat generated within electronic packages and, thus solder joint fatigue for example, various forms of heat dissipating means have been employed. One mechanism employed to facilitate heat dissipation is a heat sink positioned in thermal contact with the electronic package. Typically, the heat sink is either clamped or bonded to the semiconductor chip or cover plate.
With increasing heat generation created by smaller and denser electronic packages, improved thermal performance of heat sinks, particularly air cooled heat sinks, is required. However, with smaller electronic packaging, the thermal contact area becomes more limited. Because of the constrained X-Y contact space, heat sink structures with high aspect ratios extending further in the Z direction act to facilitate additional heat dissipation. However, manufacturing such heat sinks structures, such as tall plate fin or pin fin structures, is difficult and expensive, and the resulting structures lack flexibility in their ability to be tailored according to application. In addition, whether cooling is through forced or buoyancy-driven air cooled conditions, fins in the central portion of the heat sink typically act to provide little benefit in the cooling process.
The difficulty with known heat sink structures is that they fail to provide the thermal performance required for today""s electronic packages. Moreover, such structures also fail to provide a simple, low cost, flexible approach to cooling. Typical of known stacked heat sinks are those described in U.S. Pat. No. 5,794,684 and U.S. Pat. No. 5,900,670.
Accordingly, it is an object of the present invention to provide an improved heat sink.
It is a further object of the present invention to provide an improved heat sink structure and method for effectively dissipating heat from heat generating devices having limited thermal contact surface.
It is yet a further object of the present invention to provide an easily manufactured and readily assembled, low cost and adaptable heat sink structure and method.
It is another object of the present invention to provide a heat sink structure with improved weight/heat dissipating performance characteristics.
It is yet another object of the present invention to provide an improved heat sink structure capable of being readily adapted and extended to match the particular heat dissipating application.
In accordance with the present invention, a stacked pyramidal heat sink structure with central air passage openings is provided for improved thermal performance under either forced or buoyancy driven air cooled conditions. The heat sinks are stacked in a hierarchical arrangement with the bottom most layer having no opening or a small opening centered therein, and with each layer in the stack having a smaller opening than the opening in the next layer above it such that the openings become progressively larger as the layers build so that the top most layer has the largest centered opening. The heat sink structure may be any cooling structure having multiple vertical heat dissipating elements or surfaces extending from a base plate, such as, pin-fin, plate-fin, corrugated, and the like. It is clear that the opening in the central region of the base plate removes what would otherwise be the vertical heat dissipating elements in this region.
Convection cooling may be achieved by either forced air or buoyancy driven air cooled conditions. Under forced convection cooling, removal of fins in the central region decreases resistance to flow. Thus, for a fixed pumping power, a greater amount of flow is realized, in effect increasing the heat removed from the remaining fins. Similarly, under buoyancy-driven air cooled conditions where the heat sink base plate in contact with the heat generating surface is in a horizontal orientation, fins in the central region of the heat sink typically act to provide little benefit in the cooling process. Their removal also offers less resistance to the buoyant flow. In addition, heat sink weight is also reduced due to the removal of fins.
The stacked heat sink layers may be made from any of a variety of materials and different layers may be made of different materials with different thickness to form a composite, designed in accordance with particular application. For example, the bottom layer may be selected such that it exhibits thermomechanical properties closely matching the juxtaposed cover plate or silicon chip to avoid CTE-related mismatch effects.